The invention relates to an apparatus for raising a liquid aeration apparatus including an air distributing pipe and aeration tubes extending perpendicularly therefrom and preferably made of a ceramic material. The aeration apparatus is connected with a stationary support by a supply or supporting pipe arrangement by means of one or more joints, about which the apparatus can be pivoted. The raising apparatus also includes a cable which has a carrier element on its free end and a boom having an end disposed above the surface of the liquid over which end the cable is guided. The invention also relates to a method for raising the aeration apparatus.
In deferrization or neutralization processing of drinking and industrial water or for example in the biological cleansing of waste water, compressed air in the form of fine bubbles is injected into the liquid. In contrast to surface aeration, this type of aeration has the advantages that no aerosols are produced which might be questionable for hygenic reasons, that only a small amount of noise is produced and that there are no difficulties or limitations arising from low air temperatures. To enable the injection of the compressed air, filter bodies or so called aeration tubes are employed which today are made primarily of ceramic materials and are quite heavy. During operation it is necessary to periodically examine the aeration tubes or to clean or replace damaged tubes. For this reason the tubes are generally attached to an air distributing tube by means of screw or plug connections, whereby the air distributing pipe is attached to one or more vertical supply or support pipes. In order to provide access to the aeration tubes, the supply or support pipe apparatus is connected to a rigid support by means of one or more pivotable joints, so that the entire aeration apparatus can be rotated up out of the water. The possibility thus exists, if the aeration apparatus is not excessively heavy, that for example a hook attached to a rod can encompass the air distributing pipe in order to manually raise it from a special walkway arranged above the basin. However, the turbulance of the water causes difficulties in guiding the rod, in that there is the possibility of lateral movement parallel to the air distributing pipe in the vicinity of the aeration tubes. The solid matter in the basin also causes difficulties by hindering visibility so that it is difficult to encompass the air distributing pipe without contacting and thereby possibly damaging the aeration tubes. This type of contact with the aeration tubes is particularly to be avoided as the examined aeration apparatus is again lowered into the basin. With the ceramic materials employed, this type of manual operation is not possible because of the substantial weight of the portion of the apparatus which is located under water when in operation and is capable of being pivoted upward, namely the supply or support pipes, the distributing pipe and the aeration tubes. According to German AS No. 1,609,002, an aeration apparatus can be raised with the aid of a cable. In this process the cable is guided over the free end of a boom which in turn is arranged on a waste water trough running above the liquid in the central portion of the basin. Raising the aeration apparatus is thus only possible if the basin has special walkways above the liquid. A further requirement in order to be able to employ the raising apparatus according to German AS No. 1,609,002 is the special embodiment of the descent guide between the aeration apparatus and the area above the liquid. The descent guide may not have any joints or angles, because otherwise the carrier element arranged on the cable cannot slide down the descent guide in order to engage the aeration apparatus.
Various proposals have therefore been made to enable the aeration apparatus to be rotated up out of the liquid by means of mechanical raising devices disposed on the aeration apparatus itself. These mechanical raising devices, however, require a substantial expense for design and manufacture and are also subjected to severe corrosion because of the prevailing operating conditions which impair their long term operability (U.S. Pat. No. 2,997,284, U.S. Pat. No. 3,116,021, French Pat. No. 1,326,615, British Pat. No. 638,185).
In order to avoid these disadvantages it was proposed in German Pat. No. 2,452,574 to provide the pivotable portion of the aeration apparatus with a body which, because of its weight, can produce a torque in its range of rotation as the pivotable portion is rotated upward. This body also offers a point of attachment for a raising element in the form of for example a rod with a hook. There could be no cooperation between the hook and the air distributing pipe because this might damage the sensitive aeration tubes.
A device in accordance with German Pat. No. 2,452,574, however, clearly has the disadvantage that the body producing the torque must be very large making the arrangement expensive to design and construct.
If, however, an aeration apparatus like that described in German Pat. No. 2,452,574 had no body producing any torque in the rotational range of the aeration apparatus, the aeration basin would have to be emptied in order to clean or replace aeration tubes. This has the disadvantages that the cleaning of the waste water in the waste water basin must be interrupted, and that additional energy must be used in order to empty the basin, because normally in the cleaning of waste water the basin lies below the ground water table. This means, however, that the basin must be anchored in the ground so that in the empty condition it experiences no buoyancy which might cause it to move.